22 - Membranes and Lipids Flashcards
membrane general functions
- semipermeable barrier
- detects and interprets changes on extracellular environment
- provides anchorage sites for extracellular proteins and cytoskeleton
- provides an alternative environment to the cytoplasm
Compartmentalisation in eukaryotic cells
Eukaryotic cells are compartmentalised
Compartments are enclosed in membranes
Membrane proteins important for functions
Membrane model structure name
fluid mosaic model
what largely defines the function of a protein
largely defined by the protein molecules, lipids, and complexes that reside in it
Membrane topology - diagram
how many lipids in lipid bilayers
~5 x 10^6 lipid molecules per micrometre squared of bilayer
- plasma membrane of a typical cell contains ~10^9 lipids
different types of lipids found in membranes
Phospholipids
Glycolipids
Cholesterol
different molecules found in membranes
- how different membranes differ in their composition
- proteins, lipids and carbohydrates found in membranes
- composition of these molecules depends on membrane function and structure
- e.g. mitochondria contain large majority of protein in membrane buildup, for electron transport chain, ATP synthase, etc.
Key biological functions of lipids
- fuel for metabolism
- membranes:
- phospholipids - phosphoglycerides and sphingolipids
- glycolipids
- cholesterol
- signalling molecules
- steroid hormones, e.g. sex hormones and cortisol
- eicosanoids: short range signalling molecules involved in pain, inflammation, etc.
Vitamins: A, D, E and K
general characteristics of lipids
- lipids very diverse in structure
- defined by hydrophobocity rather than structure
- not soluble in water
- soluble in organic solvents, e.g. chloroform, ethanol, due to polarity of these substances
glycerol derivatives and their functions
- what bonds they contain
triacyl glyceride - storage of fuel for metabolism
- contain ester bonds
- phosphoglycerides - key component of biological membranes
- contain ester bonds
Phospholipids - amphipathic
- polar phosphate head is hydrophilic
- fatty acid chain are hydrophobic
- amphipathic - both preoperties in same molecule
hydrophobic parts of membranes
- they exclude water
- are extensive
- close in on themselves - no edges for contact with water - natural shape
- self-sealing
structure/properties of fatty acids
saturated fatty acids
- three systems for numbering carbons
- no C=C double bonds
different carbon numbering system: - 1, 2, 3 - chemical numbering system
- a, B, y - biochemical still used in metabolism
- w, w-1, w-2 - used in nutrition
what affects melting point of fatty acids
- melting point increases with increasing chain length
- MP decreases with increasing double bonds - more fluid
Unsaturated fatty acids
- effect on melting point
- contain C=C double bonds
- double bonds in fatty acids are usually cis
DIfference between cis and trans
- trans - almost straight
- cis - introduces a kink in the chain
- MP decreases with increasing double bonds - more fluidity
irregulat packing of fatty acids tails info
- C=C cis double bond introduces kink in the chain
- causes irregular packing of fatty acid chain
- leads to lower MP or more fluidity
What are essential fatty acids - functions
must be obtained in diet
- as have important function in cell membrane, signalling
- starting point for making arachidonic acid
Arachidonic acid info and function
- synthesised from linoleic acic
- precursor for eicosanoids (polyunsaturated fatty acids, present in neural function)
- important function as part of phospholipids in membrane
- plays important role in inflammation
- conditionally essential in diet
- Structure discovered by Ida Smedley-Maclean
Eicosanoids function
- process behind it
- important in pain and inflammation
Process:
- inflammatiry signal sent to membranes
- causes release of arachidonic acid
- followed by:
- release of other eicosanoids or release of prostaglandin (aspirin or ibuprofen needed)
Prostagladin info function
- lipids made at sites of injury or tissue damage
- control processes in dealing with injury and tissue damage
- e.g. inflammation, blood flow, blood clots etc.
How can phospholipids be modified
- phosphate groups can be modified
- different grous can be added/bonded to the phosphate head, e.g. hydroxyl, amine, etc.
Biological function of head groups in phospholipids
Phosphatidylcholine and phosphatidylinositol can be cleaved
- inositol and choline are important signalling molecules in some metabolic pathways
- they can both transmit signals into cells, etc.
two key phospholipids and uses
- phosphoglycerides -
- sphingolipids - based on sphingosine amino acids
- used in sphingomyelin, to make schwann cells and myelin sheaths
- increases speed of electrical impulse and neurone transmission
- sphingomyelin also used in signal trransduction and apoptosis
glycolipids info
- sugar containing lipids
- sugar instead of phosphate group
- can be more than one sugar unit
- in animal cells, ddrived from sphingosine, not glycerol
- sugar always on outside of the cell
Functions: immune response, cell recognition and attachment (signalling)
cholesterol in membrane general info
sterol - modified steroid
- steroids have common structure of four hydrocarbon rings
- is the only steroid in membranes (only in animals)
- has important effects on membrane fluidity
